Measuring system for a fluid flow stream

ABSTRACT

An apparatus for determining a characteristic, as velocity or direction, of a fluid flow stream. Fluid sensors generate signals which are differentially compared to produce an error signal representative of the amount of movement, for the sensors or for a fluid stream generator, which is necessary to null the system. A servomechanism produces the nulling movement in response to the error signal. The amount of movement also generates a positional signal indicating the low frequency component or steady state characteristic of the fluid flow stream. A signal adder combines the positional signal with the error signal, containing a high frequency component, to provide an indication of the instantaneous fluid characteristic.

United States Patent Corey MEASURING SYSTEM FOR A FLUID FLOW STREAM [451July 18, 1972 Primary Examiner-Jerry W. Myracle Attorney-Hofgren,Wegner, Allen, Stellman & McCord [5 7] ABSTRACT An apparatus fordetermining a characteristic, as velocity or direction, of a fluid flowstream. Fluid sensors generate signals which are differentially comparedto produce an error signal representative of the amount of movement, forthe sensors or for a fluid stream generator, which is necessary to nullthe system. A servomechanism produces the nulling movement in responseto the error signal. The amount of movement also generates a positionalsignal indicating the low frequency component or steady statecharacteristic of the fluid flow stream. A signal adder combines thepositional signal with the error signal, containing a high frequencycomponent, to provide an indication of the instantaneous fluidcharacteristic.

9 Claim, 3 Drawing Figures FLUID FLOW STREAM 30 l %\L *DIFFERENTIAL 4PRESSURE GAUGE FACTOR PATENIED JUL I 8 I972 SHEET 1 [IF 2 SERVO 1ePRESSURE GAUGE DIFFERENTIAL SCALE FACTOR 1 FLUID FLOW STREAM ADDER IDIFFERENTIAL PRESSURE GAUGE SUPPLY IK I MEASURING SYSTEM FOR A FLUIDFLOW STREAM BACKGROUND OF THE INVENTION This invention relates to ameasuring system for a relatively moving fluid flow stream, and moreparticularly to a system for measuring an instantaneous characteristicof a fluid flow stream which has both slowly changing and rapidlychanging components.

Prior apparatus for measuring the velocity or direction of a fluid flowstream typically use servomechanisms to drive an element toward a nullcondition. The position of the element is used to provide a measure ofthe velocity or direction of the fluid flow stream. While such systemsprovide the advantages of a closed loop measurement, the system isaccurate only when the element is at a null position, and hence theaccuracy is limited by the time response of the servomechanism.

An example of a typical measuring system is an aircraft angle of attacktransducer. A probe extending through the aircraft skin and into theairstream has two parallel rows of pressure ports which sense the ramjet pressure of the airstream. A differential pressure servo amplifierrotates the probe until the ram jet pressures at both rows of ports areequal. The rotational position of the probe is a direct measure of theairstream direction, which in turn can be directly related to the angleof attack of the aircraft. However, when the angle of attack changesrapidly, the indicated angle of attack lags the actual angle of attack,and a new steady state angle of attack is not correctly indicated untilthe servomechanism has had sufficient time to rotate the probe to a newposition.

SUMMARY OF THE INVENTION In accordance with the present invention, theinstantaneous direction or velocity of a fluid flow stream is determinedby apparatus which retains the advantages of a closed loopservomechanism. The apparatus may be used in any system in which acharacteristic of a fluid flow stream can be measured by movement of anelement. The measured characteristic may be fluid direction, velocity,pressure, or any other fluid characteristic for which suitable sensorsare available.

One object of the present invention is to provide apparatus formeasuring an instantaneous characteristic of a fluid flow stream.Illustratively, the characteristic may be the direction, velocity, orpressure of the fluid stream, or other characteristic which can bemeasured by a plurality of devices, at least one of which is relativelymovable.

Another object of the present invention is to provide a fluid measuringapparatus in which devices for determining a fluid characteristic arerelatively movable by a servomechanism driven by differentially comparedsignals from fluid sensors. A signal summing means combines a signalrepresenting the position of the servomechanism with the output of thedifferentially compared signals in order to indicate an instantaneouscharacteristic of the fluid flow stream.

A further object of this invention is the provision of a fluid flowstream measuring apparatus which may be added to existing measuringsystems with a minimum of modification, and which is usable both withsystems generating local effects deflected by the moving fluid flowstream and with systems dependent solely upon the moving fluid flowstream for measurement purposes.

While an illustrative embodiment of the invention is shown in thedrawings and will be described in detail herein, the invention issusceptible of embodiment in many different forms and it should beunderstood that the present disclosure is to be considered as anexempliflcation of the principles of the invention and is not intendedto limit the invention to the embodiment illustrated. The scope of theinvention will be pointed out in the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagramillustrating the invention as applied to a fluid stream velocitydetection apparatus;

FIG. 2 is a schematic diagram illustrating the invention as applied to afluid stream direction determining apparatus; and

FIG. 3 is a schematic diagram of the invention as applied to a fluidstream direction determining apparatus operating upon the ram jetprinciple.

DESCRIPTION OF THE PREFERRED EMBODIMENT In the drawings, the measuringapparatus is illustratively shown in combination with systems formeasuring airstream velocity and direction. In FIGS. 1 and 2, airstreamvelocity and direction, respectively, are determined by sensing thedeflection of transmissions exposed to the airstream. As will appear,the transmissions may be in the form of a fluid jet stream, or anacoustic wave. In FIG. 3, airstream direction is determined by thedifference in ram jet pressure on a plurality of receivers located inthe path of the airstream.

Turning to FIG. I, the present invention is illustrated in combinationwith a fluid flow stream velocity measuring apparatus of the typedisclosed in my copending application Fluidic Sensor For Fluid StreamVelocity," filed on even date herewith, Ser. No. 45,029, and assigned tothe assignee of this invention, to which reference should be made for aspecific disclosure of the principle and details of operation of theapparatus. The apparatus will be described herein only insofar as it isnecessary to an understanding of the present invention.

A supply jet nozzle I0 is axially disposed opposite two receiver nozzles12 and 14, and is initially positioned along an axis midway between thereceiver nozzles 12 and 14. The nozzle 10 is movably mounted on athreaded shaft 16 which, when rotated by a servo drive means 18, causesthe nozzle 10 to be displaced laterally along the axial direction of thethreaded member 16. Also connected to the nozzle 10 structure is an arm20 of a potentiometer having a resistance 22 connected across a voltagesupply means, such as a battery 24. As potentiometer arm 20 is movedrelative to resistance 22, the voltage at potentiometer arm 20 is variedin direct proportion to the displacement of the nozzle 10. In mycopending application, this voltage is directly coupled to an indicator26 to cause a needle 27 thereon to deflect and provide an indication ofthe velocity component of the fluid flow stream, as will appear.

A jet supply means 28 furnishes a continuous flow of fluid,

which preferably is the same as the fluid in the flow stream so as toprevent contamination or other problems, to nozzle 10 which directs thefluid transmissions across the path of the fluid flow stream towards thedetectors 12 and 14. A throttle valve 29 is located in the tubulationconnecting the supply 28 to the nozzle 10 so that the flow rate of thejet stream may be selectively regulated.

Receivers l2 and I4 are pressure sensitive devices which each generate asignal having a value dependent upon the pressure sensed at the nozzleopening therein. The pair of signals are connected to a differentialpressure gauge 30 which provides an error signal, on a line 31, having avalue proportional to the difference in fluid pressure between thenozzles 12 and 14. This error signal is coupled to an amplifier 32 whereit is amplified and fed to the servomechanism 18 which, by rotation ofthe shaft 16, causes the nozzle 10 to be displaced along the axis of theshaft.

The above described components are those disclosed and claimed in mybefore identified copending application, and form a velocity indicatorfor the fluid flow stream. When the nozzle 10 is in the position shownand there is no incident fluid flow stream, as when the apparatus ismounted to a support vehicle which is at rest, the fluid transmissionsfrom the nozzle 10 are equally directed to both of the nozzles 12 and14, resulting in equal pressures and a zero volt error signal on line31. Upon subjecting the transmissions to a fluid flow stream whichintersects it in a direction transverse to its axis, the jet stream isdiverted and equal pressures no longer appear in the receiver nozzles 12and 14. The differential pressure produces an error signal which drivesthe servomechanism 18 to rotate threaded shaft 16 and displace thenozzle 10 in a direction which tends to equalize the pressure. Movementof the nozzle 10 continues until the receivers 12 and I4 detect equalfluid pressures. As explained in the before identified application, it

can be shown that the new position of the transmitter nozzle is directlyrelated to the velocity of a fluid stream flowing normal to the jetstream emitted by the transmitter. Since the voltage on arm is directlyproportional to this position, the meter 26 may be calibrated directlyin terms of velocity, thereby indicating the velocity of the incidentfluid flow stream.

The time response of servomechanism 18 limits the use of the abovedescribed apparatus to measuring slowly changing or low frequencyvelocity components of a fluid flow stream. In order to measure theinstantaneous velocity of the fluid flow stream, the additionalapparatus in FIG. I is used to sum a high frequency velocity componentwith the existing low frequency velocity component. While a separatehigh frequen cy component could be generated, applicant simplifies thesystem by using a signal already in existence in the above describedapparatus, and which includes information as to rapidly changingcomponents of the fluid stream, namely the error signal fromdifferential gauge 30. More particularly, the error signal is alsocoupled over a line 33 to an amplifier 34, and thence through a scalefactor network 35 to a signal adder 38. The positional signal frompotentiometer 20 is also coupled to adder 38, which adds it to thescaled error signal to form a single summed signal coupled to indicator26.

When the fluid flow stream velocity has damped to a steady statecondition, transmitter 10 is located at a new position 10' which causesa given voltage at arm 20. Since equal pressures are being received atreceivers 12 and 14, no error signal is generated and hence noadditional voltage is added due to differential gauge 30. Assuming thefluid flow now increases to a new fixed velocity, a differentialpressure is sensed and, before servomechanism 18 can respond thereto,the pressure difference error signal is amplified, scaled, and is summedin adder 38 with the positional signal to indicate at meter 26 theincreased instantaneous velocity of the flow stream. As servomechanisml8 respondsto the pressure difference, the jet nozzle 10 is movedfurther from the null position, increasing the signal at arm 20.However, this causes the error signal to decrease, so that the sum ofthe two signals remains constant. As the servomechanism nulls, the errorsignal on line 33 goes to zero, and the signal from wiper arm 20 aloneprovides the indication of the velocity of the fluid flow stream.

Certain modifications may be made in the velocity determining apparatuswithout changing the manner in which the present invention is utilizedtherewith. For example, in place of the translatable jet nozzle 10, thetransmitter may remain fixed and the pair of receiver nozzles 12 and 14may be displaced by a servomechanism. In such a case, the potentiometerarm would be connected to move with the receiver nozzles.

In FIG. 2, the invention is shown in combination with apparatus formeasuring the direction of a fluid flow stream. Direction determiningapparatus of this type is disclosed in my copending application FluidicDirection and Velocity Detection Apparatus, filed on even date herewith,Ser. No. 45,016,

and assigned to the assignee of the present invention. For a morecomplete description of the theory and operation of the system, alongwith possible alternatives, reference should be made to the aboveapplication, which will be described herein only insofar as it isnecessary to an understanding of the present invention.

A jet supply nozzle 40 is fixedly mounted relative to a pair of receivernozzles 42 and 44, the three devices being mounted on a platform 46which is relatively movable with respect to the fluid flow stream.Connected to jet nozzle 40 through suitable tubulation is a jet supplysource 48, the flow rate of which may be regulated by a valve 50. Thereceiver nozzles 42 and 44 are similar to the nozzles 12 and 14 in FIG.I, and are connected to a similar differential pressure gauge 52 toproduce an output error signal, on a line 53, proportional to thedifference in pressure sensed at nozzles 42 and 44. The error signal isamplified by an amplifier 54 and coupled to a servomechanism 56 forrotating the platform 46 by means of a drive gear mechanism 58.

To monitor the fluid flow direction, a potentiometer 60 has an arm 62connected for movement with platform 46. Potentiometer 60 is connectedacross a DC voltage source, as a battery 64. The voltage signal at arm62 is coupled to a meter 66 having a needle 67 deflected in proportionto the signal input, in the same manner as meter 26 in FIG. 1.

The above described apparatus of FIG. 2 is that disclosed in my lastidentified copending application. In operation, the valve 50 is openedto form a fluid jet stream which impinges equally on receiver nozzles 42and 44 when the direction of the fluid flow stream is parallel with thedirection of the jet stream transmissions. However, should unequalpressures be detected in the receivers 42 and 44, as is the case whenthe fluid flow stream has a directional component transverse to thedirection of transmissions, as shown by the dashed lines, the jet streamis diverted and causes differential gauge 52 to produce an error signal.The servo 18 rotates platform 46, counterclockwise for the new fluiddirection illustrated in dashed lines in FIG. 2, until equal pressuresare sensed at nozzles 42 and 44. At this time, the jet stream is aligneddirectly with the incident fluid flow stream.

In accordance with the present invention, the additional apparatus shownin FIG. 2 is provided to indicate the instantaneous direction of thefluid flow stream. The amplified error signal is coupled to a scalefactor network 70 which has an output coupled to an adder 72. The adder72, like the adder 38 in FIG. 1, combines the positional or lowfrequency component signal from arm 62 with the error or high frequencycomponent signal. The summation of the signals is coupled to meter 66 inorder to provide an instantaneous indication of the direction of thefluid flow stream.

Modifications may be made in the direction determining apparatus withoutchanging the disclosed instantaneous measurement system. If desired, theapparatuses of FIGS. 1 and 2 may be combined into a single combineddirection and velocity indicating system, in which the servo 56 of FIG.2 is used to rotate the velocity determining apparatus of FIG. 1 so asto maintain the jet transmissions therefrom at all times perpendicularto the direction of the incident fluid flow stream. While the systems ofFIGS. 1 and 2 have special advantages when measuring fluid flow streamsof low velocities, difi'erent apparatus may be used when the fluid flowstream velocity is of greater magnitude. For example, the transmissions,here in the form of a fluid jet stream, may be in the form of anacoustic wave. Such a system is disclosed in my copending applicationDirection and Velocity Determining Apparatus, Ser. No. 809,837, filedMar. 24, 1969, and assigned to the same assignee of the presentinvention.

In FIG. 3, the present invention is applied to a direction determiningapparatus operating on a different theory than that shown in FIG. 2. Theapparatus of FIG. 3 employs the ram jet principle, and is commonly usedto detect airstream direction relative to an air frame reference, i.e.,an angle of attack transducer. As illustrated, the apparatus consists ofa probe which extends longitudinally beyond the skin 81 of the aircraft.Probe 80 includes a parallel row of pressure ports 83, and a secondparallel row of pressure ports 84, spaced from the ports 83. The twoparallel rows form equal angles from the airflow stagnation point tosense the differential ram jet pressure against the ports as theaircraft moves through the airstream. The ports 83 are connected througha tubing 85 to a differential pick-off 87. The second row of ports 84are connected through a tubulation 88 to the differential pick-off 87.The output from device 87, as is well known, is an error signal, on aline 90, which is proportional to the difference in pressure betweenports 83 and ports 84. The signal is amplified by an amplifier 9] havingan adjustable gain control 92, and coupled to a servomechanism motor 93which by means of gear ing 94 repositions or rotates the probe 80 withinbearings 96, 97 to a balanced pressure position.

The motor 93 also causes a wiper am 100 of a potentiometer 101 to movean amount proportional to the movement necessary to reposition the probe80. The resistance 101 of the potentiometer is coupled across a sourceof voltage, such as a DC battery 103, thereby generating a voltagesignal on arm 100 which is coupled to an indicating meter 107 and tounits for controlling the aircraft.

in accordance with the present invention, the error signal to servomotor 93 is also coupled to a scale factor network 114 to produce ascaled output connected to an adder network 116. The other input ofadder 116 is the positional signal from arm 100. The adder 116,operating in the same manner as the adder 72 in FIG. 2, sums thepositional signal with the scaled error signal in order to provide anoutput signal to meter 107 which indicates the instantaneous directionor angle of attack of the airstream. Thus, it will be seen that theinvention can also be used when the devices for determining thecharacteristic of fluid consists of only a pair of elements fixed withrespect to each other but movable with respect to the fluid stream.Other modifications will be apparent to those skilled in the art.

lclaim:

1. Apparatus for measuring a characteristic of a fluid flow stream,comprising:

device means for generating'a pair of signals differentially influencedby said fluid flow stream and by movement of at least part of saiddevice means, means movably mounting said part of said device means formovement to different positions representing different values of saidfluid characteristic; differentially responsive means coupled to saiddevice means for generating an error signal having a value proportionalto the difference between the signals from said device means;

servo means coupled to said differentially responsive means for movingsaid movable part of said device means to tend to null said errorsignal;

position responsive means for generating a positional signal whichrepresents the instantaneous position to which said servo means hasmoved said movable part of said device means; and

summing means for combining said error signal and said positional signalto provide a measurement of the instantaneous characteristic of saidfluid flow stream.

2. The apparatus of claim l wherein said device means comprisestransmitter means and at least two receiver means, said transmittermeans emitting transmissions along an axis exposed to said fluid flowstream, said transmission deviating in direction when the fluid flowstream is incident thereon, said receiver means being axially spacedfrom said transmitter means for detecting said transmissions and eachgenerating a signal varying as the transmissions deviate in directionfrom said axis, said servo means changing the relative spacing of saidtransmitter means and said receiver means.

3. The apparatus of claim 2 for measuring the velocity characteristic ofthe fluid flow stream, wherein said transmitter means emitstransmissions along an axis generally perpendicular to the direction ofthe fluid flow stream, said servo means moving one of said transmittermeans or said receiver means relative to the other so as to change therelative spacing therebetween, whereby said summing means provides ameasurement of the instantaneous velocity of said fluid flow stream.

4. The apparatus of claim 3 wherein said position responsive meansincludes potentiometer means having an arm coupled to said one means forchanging a resistance of the potentiometer in proportion to movement ofthe one means, electrical supply means coupled to said resistance tocause the voltage at said arm to form said positional signal, saidsumming means including a meter for indicating the total signal coupledthereto, and a signal adder having inputs coupled to said potentiometerarm and said differentially responsive means to provide a measurement ofthe instantaneous velocity of the fluid flow stream.

5. The apparatus of claim 2 for measuring the directional characteristicof the fluid flow stream, wherein said transmitter means emitstransmissions along an axis which is to be maintained parallel to saidfluid flow stream, platform means fixedly mounting said transmittermeans relative to said receiver means, said servo means rotating saidplatform means to positions which maintain said fluid flow streamparallel to said transmissions, thereby providing a measurement of theinstantaneous direction of said fluid flow stream.

6. The apparatus of claim 5 wherein said summing means includes a scalefactor network coupled to said differentially responsive means forsealing said error signal which represents a high frequency directionalcomponent of said fluid flow stream.

7. The apparatus of claim 2 wherein said transmissions consist of a jetstream of fluid of the same composition as the fluid of said fluid flowstream, said receiver means being responsive to the pressure of thefluid incident thereagainst.

8. The apparatus of claim 1 wherein said device means comprises at leasta pair of pressure sensitive means each generating a signal inproportion to the ram pressure of said fluid flow stream thereagainst,probe means mounting said pressure sensitive means fixed with respect toeach other, bearing means mounting said probe means movable with respectto said fluid flow stream, said servo means moving said probe means tobalance the ram pressures at said pressure sensitive means.

9. The apparatus of claim 8 wherein said position responsive meansincludes a signal generating means for producing a signal having anamplitude dependent upon the position of a movable element, meanscoupling said movable element to said servo means for movement withmovement of said probe means, and said summing means includes a scalefactor network for at least one of said signals.

1. Apparatus for measuring a characteristic of a fluid flow stream,comprising: device means for generating a pair of signals differentiallyinfluenced by said fluid flow stream and by movement of at least part ofsaid device means, means movably mounting said part of said device meansfor movement to different positions representing different values ofsaid fluid characteristic; differentially responsive means coupled tosaid device means for generating an error signal having a valueproportional to the difference between the signals from said devicemeans; servo means coupled to said differentially responsive means formoving saId movable part of said device means to tend to null said errorsignal; position responsive means for generating a positional signalwhich represents the instantaneous position to which said servo meanshas moved said movable part of said device means; and summing means forcombining said error signal and said positional signal to provide ameasurement of the instantaneous characteristic of said fluid flowstream.
 2. The apparatus of claim l wherein said device means comprisestransmitter means and at least two receiver means, said transmittermeans emitting transmissions along an axis exposed to said fluid flowstream, said transmission deviating in direction when the fluid flowstream is incident thereon, said receiver means being axially spacedfrom said transmitter means for detecting said transmissions and eachgenerating a signal varying as the transmissions deviate in directionfrom said axis, said servo means changing the relative spacing of saidtransmitter means and said receiver means.
 3. The apparatus of claim 2for measuring the velocity characteristic of the fluid flow stream,wherein said transmitter means emits transmissions along an axisgenerally perpendicular to the direction of the fluid flow stream, saidservo means moving one of said transmitter means or said receiver meansrelative to the other so as to change the relative spacing therebetween,whereby said summing means provides a measurement of the instantaneousvelocity of said fluid flow stream.
 4. The apparatus of claim 3 whereinsaid position responsive means includes potentiometer means having anarm coupled to said one means for changing a resistance of thepotentiometer in proportion to movement of the one means, electricalsupply means coupled to said resistance to cause the voltage at said armto form said positional signal, said summing means including a meter forindicating the total signal coupled thereto, and a signal adder havinginputs coupled to said potentiometer arm and said differentiallyresponsive means to provide a measurement of the instantaneous velocityof the fluid flow stream.
 5. The apparatus of claim 2 for measuring thedirectional characteristic of the fluid flow stream, wherein saidtransmitter means emits transmissions along an axis which is to bemaintained parallel to said fluid flow stream, platform means fixedlymounting said transmitter means relative to said receiver means, saidservo means rotating said platform means to positions which maintainsaid fluid flow stream parallel to said transmissions, thereby providinga measurement of the instantaneous direction of said fluid flow stream.6. The apparatus of claim 5 wherein said summing means includes a scalefactor network coupled to said differentially responsive means forscaling said error signal which represents a high frequency directionalcomponent of said fluid flow stream.
 7. The apparatus of claim 2 whereinsaid transmissions consist of a jet stream of fluid of the samecomposition as the fluid of said fluid flow stream, said receiver meansbeing responsive to the pressure of the fluid incident thereagainst. 8.The apparatus of claim 1 wherein said device means comprises at least apair of pressure sensitive means each generating a signal in proportionto the ram pressure of said fluid flow stream thereagainst, probe meansmounting said pressure sensitive means fixed with respect to each other,bearing means mounting said probe means movable with respect to saidfluid flow stream, said servo means moving said probe means to balancethe ram pressures at said pressure sensitive means.
 9. The apparatus ofclaim 8 wherein said position responsive means includes a signalgenerating means for producing a signal having an amplitude dependentupon the position of a movable element, means coupling said movableelement to said servo means for movement with movement of said probemeans, and said summing means includes a scale factor network for atleast one of said signals.